.

Also, why did Lord Vishnu sleep on snake?

His name means "that which remains", from the Sanskrit root sis, because when the world is destroyed at the end of the kalpa, Shesha remains as he is. So he is refered as "Ananta-Shesha" which means "Endless Shesha". Lord Vishnu is seen resting on the coils of the serpent Shesha, also called Ananta.

Subsequently, question is, who is sheshnag wife? Revati

Considering this, who was Vasuki?

Vasuki. Vāsuki is a serpent king in Hindu and Buddhist religion. He is described as having a gem called Nagamani on his head. Manasa, another naga, is his sister. Vāsuki is Shiva's snake.

Is Vasuki and Sheshnag same?

So i think Lord Shesha and Lord Shiva are same. Lord Kulki will come for Destruction so He is incarnation of Lord Shiva (Shesha),but he is part of Lord Mahvishnu. Lord Vishnu is born God and Lord Shesh (Shiva) is mortal became god. Shesha is Spacetime And Vasuki is life.